Self-regulation failure has been implicated in the development of obesity in children. Little is known, however, about the extent to which children's stress responses (a marker for self-regulation) in infancy and early childhood predict body mass index trajectories, nor do we fully understand the ways in which children's bio-behavioral responses to stress, including eating in response to stress, influence adverse weight outcomes. The mechanisms by which children's biological stress responses and behavioral self-regulation are linked to obesity are largely unknown; we propose that dysregulated eating is one key mechanism. The proposed study takes an integrated, bio-psychosocial, developmental approach to examining behavioral, biological, and eating regulation as key bio-behavioral underpinnings of obesity in rural children. Building on data collected from birth through grade 5 as a part of the ongoing Family Life Project (Children in Rural Poverty: Risk and Protective Mechanisms), we propose to examine bio-behavioral mechanisms involved in the development of obesity in young children. The Family Life Project is a multi-site, longitudinal study which examines distal and proximal influences on rural children's development. Data were collected on ~1300 infants and their caregivers at study entry, and more than 1,000 children have been followed through grade 5. In addition to measures on children's stress response, behavioral self-regulation, and body mass index (BMI), a number of parental and family environmental factors have been collected on children since birth. Using a planned missingness design, we propose to collect new information from 750 families on children's (mean age = 12yrs) biobehavioral and eating regulation in response to stress, and their relations with family environment and obesity. An experimental study (in a subset of 375 families) will provide a unique opportunity to examine the causal effects of stress on eating behavior and self-regulation under standardized conditions. We will also examine the influence of early exposure to family adversity (e.g., harsh parenting and household chaos) on children's regulatory capacity, and the trajectory of BMI from age 24 mos to 12yrs. We will also examine the extent to which individual characteristics (e.g., race) and biobehavioral predisposition to obesity (maternal weight status and stress regulation) moderate these relations. While several studies have outlined various behavioral and environmental influences on children's development of obesity, the proposed study will objectively measure children's capacity to self-regulate in several domains of development, and will examine the extent to which family and household factors contribute to self-regulatory capacity, and its potential influence on children's BMI trajectory and obesity development from early childhood to adolescence.